Power distribution system for microwave process chambers



' y 1966 M. R. JEPPSON ETAL 3,263,052

POWER DISTRIBUTION SYSTEM FOR MICROWAVE PROCESS CHAMBERS Filed Sept. 11,1963 2 Sheets-Sheet 1 INVENTORS MORR/S R. JEPPSON BY FRANKLIN J. SMITH ATTOR/VEY y 1956 M. R. JEPPSON ETAL 3,263,052

POWER DISTRIBUTION SYSTEM FOR MICROWAVE PROCESS CHAMBERS Filed Sept. 11,1965 2 Sheets-Sheet 2 :EIE-ILS MICROWA VE GE IVE RA TO)? SOURCEINVENTOR.

MORRIS R. JEPPSO/V BY FRANKLIN J. SM/TH A TTORNE Y United States Patent3,263,052 POWER DISTRIBUTION SYSTEM FOR MICRO- WAVE PROCESS CHAMBERSMorris R. .leppson, Alamo, and Franklin J. Smith, Danville, Califi,assignors to Cryodry Corporation, San

Ramon, Calif., a corporation of California Filed Sept. 11, 1963, Ser.No. 308,284 8 Claims. (Cl. 219-1055) The present invention relates toapparatus for treating products with microwave energy and moreparticularly to a microwave energy distributing system for processingchambers.

Microwave energy has recently been applied to the processing ofsubstances for a variety of purposes. As such energy penetratesdielectric materials and readily heats any water contained therein,microwave irradiation provides a very rapid and efficient means forcooking foods, freeze drying foods, and for drying or heat treating manyother products such as paper, wood, and a variety of industrialchemicals. A representative process involving the treatment ofsubstances by microwave irradiation is disclosed in copendingapplication Serial No. 274,648, filed April 22, 1963, now abandoned, byMorris R. Jeppson and entitled, Process for Sterilizing Food Products.

Processes of the type discussed above generally require a heatingchamber in which the product is disposed for irradiation. By means of awaveguide or other transmission means, microwave energy is injected intothe chamber which has conducting walls so that the energy is reflectedand repeatedly passes through the product. The detailed structure andmode of operation of a heating chamber of this class is disclosed incopending application Serial No. 245,010, filed December 17, 1962, nowabandoned, by Morris R. Jeppson and entitled, Continuous ProcessMicrowave Heating Chamber.

In order to process substances rapidly and to obtain other advantageousresults, it is generally desirable to provide for a high intensity ofmicrowave irradiation. However, the rate at which such energy can beinjected into the chamber through a single ordinary waveguide isgenerally limited to a value which is much less than the optimum fromthe process standpoint. This limitation arises from voltage breakdown atthe region where the waveguide opens into the chamber and is primarilydue to the concentration of power at this point. Breakdown, in the formof arcing or other types of electrical discharge, must be prevented asit consumes power and may severely damage the equipment.

Although this limitation on power injection is present in varyingdegrees in most types of microwave chamber process, it is particularlysevere where microwaves are used to acceleratethe freeze drying offoods. In this process heat is supplied to a frozen food product withina vacuum environment. The water content of the food is thereby caused tosublime directly from the frozen phase to vapor in which form it iswithdrawn from the product. Microwaves provide a particularly efiicientmeans for supplying heat to the product as such energy penetrates theproduct and preferentially heats the ice crystals therein. A difiicultyin using microwave energy for this purpose results from the fact thatthe vacuum within the heating chamber promotes breakdown and sparking,near the point of injection, at very low power levels.

At the microwave frequencies most useful for freeze drying, 400 to10,000 megacycles, discharges tend to occur at power levels of less thanone kilowatt where a single conventional feed is employed. The mostefficient application of microwave energy to freeze drying requires theinjection of tens to hundreds of kilowatts into the heating chamber.

In other microwave irradiation processes, which do not require a vacuumin the heating chamber, different factors tend to promote electric fieldbreakdown at less than optimum power levels. Where such energy is usedto accelerate the drying of foods, chemicals, wood or the like atatmospheric or higher pressures, the presence of water vapor near asingle high power microwave injection opening leads to sparking.

The difiiculties discussed above are overcome in this invention bydividing the total power input into many small separate increments whichare injected into the heating chamber at a plurality of spaced apartpoints. In addition to overcoming the limitation on power input, adistributed injection of microwaves has the further advantage ofproviding for a more uniform or, controlled heating of the productthroughout the volume of the heating chamber. This elfect isparticularly desirable where the heating chamber is a long tunnelthrough which products are continuously carried by a conveyer asdescribed in the previously identified copending applications.

While it is possible to obtain a distributed input of power by couplinga large number of small microwave sources to the heating chamber throughan equal number of spaced apart waveguides or the like, severalpractical difliculties are involved. Such a heating chamber is complex,costly and subject to considerable maintenance requirements relative toone which is coupled to a single high power microwave generator or to asmall number of such sources. A very pronounced difliculty is that ofinteraction between the several power sources. Power from one source maybe coupled back into another with possible severe damage thereto.

The present invention overcomes the several problems discussed above byproviding a simple and efiicient system in which the output of a highpower microwave source is divided into many small increments andinjected into a heating chamber at a plurality of spaced apart points.

In accordance with the present invention, energy from a high powersource is coupled to a microwave chamber through a very long waveguideor transmission line means which extends along the product irradiationregion. The

waveguide may itself form a portion of the chamber wall where thisconstruction is convenient. To provide for a distributed injection ofenergy into the chamber, the wall of the waveguide which faces theproduct irradiation region of the chamber is open at a plurality ofpoints along the length thereof. The waveguide wall may, for

example, be provided with a large number of spaced apart slots which aredirected transverse to the axis of the guide or may have openings withother configurations aswill hereinafter be discussed.

The openings interrupt the systematically varying current sheet whichexists in the wall of an excited waveguide. Owing to the interruption ofthe current, a time varying electrical field and accompanyingperpendicular magnetic field exists across each opening causing aportion of the microwave energy to be radiated therethrough toward theproduct region of the chamber. The emission of energy through theopenings in the above described arrangement does not conform to thatpredicted by antenna theory for radiation into free space. Where theenergy is injected into a process chamber, the size of the openingsshould be greater than that determined by theory.

While the waveguide has been described as having openings in a wallthereof, it should be understood that these need be openings in theelectrical sense only, i.e., the electrical conductor of the waveguidewall is absent at the opening area. If necessary, where energy is to bein- Patented July 26, 1966' jected into a vacuum or pressurized chamber,for example, the openings may be physically closed by windows ofdielectric material such as glass, ceramic or plastic.

In other applications, no closure is provided and the waveguide isutilized as a highly efficient means for injecting or withdrawing gasesat the chamber. This function need not interfere with the electricaloperations. Where the waveguide is utilized for gas injection, the flowacts to prevent Water vapor from approaching the injection region andthus further inhibits sparking.

The above described energy injection structure may be used withvirtually any type of microwave chamber and serves to maximize the rateat which energy can be injected without field breakdown. By anappropriate variation in the size and spacing of the openings along thewaveguide, the relative amounts of energy injected into differentportions of the chamber may be controlled. By substituting differentwaveguides on a given chamber, the distribution of power therein may bemodified as is sometimes desirable where the chamber operates on acontinuous process basis and is used for treating different products.

As a further advantage, two or more such energy distributing waveguidesmay be employed on a single chamber without any significant interferencebetween the two microwave sources.

Accordingly, it is an object of this invention to facilitate theprocessing of substances by exposure to microwave energy.

It is another object of the invention to provide a more eflicient meansfor injecting microwave energy into a processing chamber.

It is another object of the invention to minimize the the difficultiesand limitations which arise from electrical field breakdown in amicrowave processing chamber.

It is still another object of the invention to provide means forincreasing the amount of microwave power which can be fed into aprocessing chamber.

It is still another object of this invention to provide a means forobtaining a desired distribution of energy within a microwave chamber.

It is a further object of the invention to provide a system with whichmicrowave energy from a plurality of sources can be injected into aprocess chamber without significant interaction between the sources.

It is a further object of the invention to provide a means for dividingthe output of a microwave power source for injection into a processingchamber at a plurality of spaced apart regions thereof.

The invention, together with further objects and advantages thereof,will be better understood by reference to the following specificationtaken in conjunction with the accompanying drawings of which:

FIGURE 1 is a broken out elevation view of a continuous processmicrowave chamber having the present invention embodied therein,

FIGURE 2 is a cross-section view of the chamber of FIGURE 1 taken alongline 22 thereof,

FIGURE 3 is a perspective view showing a modification of the waveguidefor use with a chamber which must be hermetically sealed from thewaveguide,

FIGURE 4 is a perspective view of a section of the waveguide structurewhich supplies power to the chamber of FIGURES 1 and 2,

FIGURE 5 is a perspective view showing a second modification of thewaveguide for varying the power density along the chamber,

FIGURE 6 is an elevation section view of a second form of microwaveprocessing chamber embodying the invention, and

FIGURE 7 is a cross section view taken along line 77 of FIGURE 6.

Referring now to the drawing and more particularly to FIGURES 1 and 2thereof, there is shown a microwave heating chamber 11 of the generaltype described in the hereinbefore identified copending applicationSerial No. 245,010, the chamber being suitable for treating substanceson a continuous process basis.

The primary heating region of chamber 11 is formed by a long horizontaltunnel 12 which is of rectangular cross section and which haselectrically conducting walls. Tunnel 12 is extended at each end byterminating sections 13 and 13 which function to suppress the escape ofmicrowave energy from the ends of the chamber 11. As described in detailin copending application Serial No. 245,010, each termination 13 has aninner wall 14 which is of rectangular cross section and which forms anextension of the through passage of tunnel 12. Spaced outwardly from thedielectric wall 14 is a conducting outer Wall 16 and a volume of water17 or other lossy liquid is contained therebetween. As the microwaveenergy is injected at right angles to the axis of tunnel 12, it tends topropagate toward the ends of the tunnel by repeated refiections betweenopposite walls thereof. Upon reaching the terminating sections 13, suchenergy must repeatedly pass through the lossy liquid 17 and is thereforeattenuated rather than being emitted from the tunnel.

The product to be treated, which may be containers of food 18 to beheated, for example, is carried through tunnel 12 by a continuous beltconveyor 19 formed of dielectric material. Conveyer 19 may be mounted onrotating drums 21 disposed one at each end of the tunnel with drivebeing applied to one of the drums in the direction indicated by arrow22.

Considering now the means by which microwave energy is injected into thechamber, a long Waveguide 23, of rectangular cross-section in thisinstance, extends along the upper surface of tunnel 12. The waveguide 23may form an integral part of the wall of tunnel 12 by being fitted in amatching slot formed in the wall thereof.

Waveguide 23 receives power from a suitable conventional source 26coupled to one end thereof, the opposite end of the waveguide beingclosed.

A series of openings, such as transverse slots 27, are spaced along thewall of waveguide 23 that faces the interior of tunnel 12 to provide forthe distributed injection of energy from generator 26 into the tunnel.Factors affecting the selection of a suitable configuration and spacingfor the slots 27 will be hereinafter discussed in greater detail, thegeneral effect of the slots being to divide the microwave energy fromsource 26 into increments which are directed downwardly into tunnel 11at spaced points along the length thereof. The energy is repeatedlyreflected between the opposing walls of the tunnel 12 and thus thecontents of the containers 18 is continually penetrated by themicrowaves. In passing through the contents of the containers, a portionof the energy is absorbed with consequent heating thereof.

As will be discussed in greater detail, the injected energy willusually, to some extent, be directed obliquely with respect to the axisof tunnel 11. It is desirable to counteract this tendency as such energypropagates rapidly toward the ends of the tunnel with a reduced numberof passages through the product. Accordingly, a series of sheetreflectors 28, formed of electrically conducting material, are mountedtransversely in tunnel 12 at intervals along the length thereof. Thereflectors 28 in this example extend downwardly from the top wall oftunnel 11 to a level just above the tops of the containers 18. Otherreflector orientations and configurations may be employed where it isdesirable to concentrate the energy at some particular region of thetunnel or to overcome an undesired intensity pattern.

In some microwave chamber operations, it is necessary to provide meansfor preventing the migration of water vapor from the product to themicrowave input as such vapor will promote sparking with consequentenergy dissipation and possible damage to electrical components. Inaddition, some processes may call for the maintenance of a controlledatmosphere with the heating chamber. It

may, for example, be desirable to pass a flow of warm dry air throughtunnel 12 to further promote rapid drying of a product.

Both of the above discussed objectives may be accomplished by providingvery small perforations 29 in a wall of waveguide 23 which communicatewith a housing 31 formed on the outer side of the waveguide. Housing 31is in turn connected to a source 32 of the gas, such as dry air, whichis to be introduced into tunnel 12. The apertures 27 of the waveguide 23distribute the gas along the length of the tunnel 12 and the flow ofsuch gas through the apertures prevents water vapor from entering themicrowave source and distribution system. Provided that the perforations29 are of sufficiently small dimensions relative to the wavelength ofthe microwave energy, no significant amount of power is released intothe housing 31.

In operations Where it is unnecessary to provide a controlled flow ofgas through tunnel 12, other means may be employed to seal off themicrowave supply. As shown in FIGURE 3, inserts 33 may be disposed inthe apertures 27 of waveguide 23. Provided the inserts 33 are formed ofa suitable dielectric material such as glass, ceramic or insulativeplastic, no significant interference with microwave injection occurs.

Referring now to FIGURE 4, the slotted waveguide 23 may be considered asa form of antenna coupled to the conductor walled chamber defined by thetunnel 12. Under this condition the slots or apertures 27 will notfunction precisely as would be predicted by antenna theory for radiationinto free space but, in general, must be somewhat enlarged. As arigorous mathematical computation of the optimum aperture configurationfor a specific chamber would be unduly complex, a suitable arrangementis best determined empirically, using antenna theory criteria as astarting point. A trial waveguide may be constructed and appropriatechanges made according to the observed density and distribution ofenergy within the chamber. This may readily be done by taking intoaccount certain general properties of the apertured waveguide.

A slot cut in a conducting wall of a waveguide becomes a radiator whenit is energized by a magnetic field parallel with its length. The slotis the magnetic counterpart of the electric dipole, and resonance anddipole radiations occur when the slot has a length near M2 where A isthe wavelength of the microwave.

Aperture configurations other than that shown in FIG- URE 4 willfunction to radiate energy from the waveguide. For example, a shuntinclined slot may be cut obliquely in the narrower wall of the waveguideor a shunt displaced slot may be provided in the broad wall thereofasymmetrically with respect to the axis of the waveguide. The powerradiated by a slot is proportional to its conductance which in turn iscontrolled by the inclination of the slot in the shunt inclined case andby the displacement from the center of waveguide wall in the shuntdisplaced case. Still another aperture variation is a series inclinedslot which is cut in the broadwall of the waveguide at an angle to theaxis thereof.

Slot configurations which are in effect combinations of the foregoingcases may be employed to obtain specialized properties. Cross shapedapertures or circular apertures in the broad wall of the waveguide forexample will radiate an elliptically polarized wave.

A series of 2 slots spaced at Ag/ 2 intervals is a resonant array withthe slots effectively in parallel. This arrangement produces a radiationpattern which is normal to the waveguide or at right angles to the axisof the associated chamber. This characteristic is desirable in microwavechamber operations. However, the resonant array requires precisiontuning of the system as frequency variations from the design value causerapid changes in the input admittance.

Spacing the slots at other than Ag/2 produces a nonresonant array whichis less sensitive to minor changes in electrical parameters. Such anarrangement remains well matched over large frequency changes and theattenuation and phase change coefficients can be controlled withconsiderable arbitrariness by changing the waveguide and slot dimensionsand slot spacing. Although this arrangement results in the injection ofenergy at an angle with respect to the axis of the associated tunnel,this effect can be largely compensated for by the use of the reflectorsas hereinbefore described and can be minimized by using waveguidedimensions close to cut-off.

The waveguide may also be constructed with a single longitudinal slotwhich will radiate energy. Such a slot will generally be in the narrowwall of the waveguide but may be in the broadwall, and still radiate, ifthere is a volume of dielectric material adjacent the slot. Thedielectric material may be the hermetic closure hereinbefore discussed.The amount of radiation from ditferent sections of the uniform slot maybe controlled by varying the width thereof.

As an example, a rectangular waveguide of the transverse slot form shownin FIGURE 4 has been successfully employed in conjunction with a chamberfor heating foods by microwave irradiation. The chamber was eight feetlong, twelve inches high and eighteen inches wide. The active length ofthe associated waveguide, arranged as shown'in FIGURES 1 and 2, was fivefeet. The slots 27 were inch wide and spaced inch apart. At one end ofthe Waveguide the slots were 1.2 inches in length and increased to alength of 2.2 inches at the opposite end thereof.

By varying the length, or other dimensions, of the apertures 27 alongthe length of the waveguide as discussed above, the density of energy atdifferent portions of the length of the associated tunnel 12 may becontrolled. FIGURE 5 shows a waveguide 23 as modified for this purpose,a first portion of the slots 27 being larger than the adjacent series ofslots 27" in order to radiate more energy. Such an arrangement is highlyuseful for many microwave processes, such as drying products, wherein asubstance should be initially subjected to the maximum irradiation andsubsequently subjected to less energy as the water content of theproduct decreases in passage through the chamber.

It will be apparent that forms of microwave transmission means otherthan the hollow waveguide herein discussed may be utilized for thepurposes of the invention provided that such transmission means is of atype capable of emitting microwave energy from distributed points alongthe length thereof. Coaxial lines, strip lines, and the like can beadapted for this purpose.

Summarizing the operation of the apparatus, with reference again toFIGURES 1 and 2, the product to be treated, such as containers of food18, is continuously fed onto conveyer 19 and passes through the tunnel12. Microwave energy from source 26 is transmitted to the chamber bywaveguide 23 and injected downwardly into the tunnel 12, at a pluralityof points distributed along the length thereof, through the waveguideapertures 27. As a non-resonant array is employed in this embodiment,the tendency for energy to be injected toward the ends of the tunnel iscompensated for by the reflectors 27 as hereinbefore described.

' The principles of the invention may be applied to forms of processingchamber differing considerably from the example hereinbefore described.Referring now to FIGURES 6 and 7 for example there is shown a verticaldrying tower 34 for processing granular, particulate or liquid products.The form of tower shown in FIGURES 6 and 7 utilizes a combination ofmicrowave heating and a Warm dry gas flow to effect drying of theproducts which may, for example, be onions, wood chips, potato flakes,citrus powders, apples, or chemicals. This combination of dryingtechniques is particularly eflicient in that the microwave heating, incontrast to prior forms, establishes a temperature gradient in theproduct which is highest at the center thereof, thereby expediting themigration of moisture to the surface of product where it is removed byevaporation into the dry gas atmosphere.

Tower 34 is provided with an upright cylindrical casing 36 formed ofelectrical conductor material and having upper and lower end closures 37and 38 respectively. To provide for the input of the product which is tobe treated, a feed pipe 39 is transpierced through the upper closure 37and projects a distance downwardly into casing 36 along the axisthereof. In some instances, such as a tower designed for the treatmentof liquid products, the feed pipe may be extended completely through thecasing 36, provided that it is formed of a dielectric material which canbe penetrated by microwaves.

A product output pipe 41 is transpierced through the lower closure 38,coaxially with respect to casing 36, and connects with a flaring conicalreceiver 42 disposed inside casing 36 immediately above the lowerclosure and in position to collect the product which has dropped alongthe axis of the casing as indicated by arrow 43.

A source 44 of heated dried gas, which may be air, for example, isconnected with the lower end of casing 36 through a conduit 46 andcontrol valve 47. A gas flow outlet conduit 48 is connected to the topof the casing 36 and may lead to a vent or to source 44 for recycling.To prevent the accumulation of product at the bottom of casing 36 and toprovide for a uniform gas flow, a conical baflle 51 is disposedcoaxially in the lower portion of the casing. Baflie 51 has an upper endwith a diameter equal to that of the casing and a narrower lower endwhich extends a distance downwardly into receiver 42 in spaced relationtherefrom. Similarly, an annular baflle 52 is secured coaxially incasing 36 immediately beneath gas outlet conduit 48 and is formed with adownwardly projecting central section 53 which encircles product inputpipe 39 in spaced relation thereto.

Considering now the means for a distributed input of microwave power tocasing 36, three waveguides 54 are disposed within the casing inparallel relationship to the axis thereof. Waveguides 54, which are ofcircular cross section in this embodiment, are equidistantly spaced fromthe axis of casing 36 and equiangularly disposed therearound. The upperend of each Waveguide 54 is angled and projects through the wall ofcasing 36 to connect with a separate microwave generator 56 for eachwaveguide.

A series of slots 57 are provided in each waveguide 54 on the sidesthereof which face the center of the casing 36, the slots having :aconfiguration, spacing and dimensions determined by the considerationshereinbefore discussed.

An advantage of the circular geometry of this embodiment is that theinjected power is concentrated at the axis of the chamber along whichthe product passes. The embodiment illustrates still a further advantageof the invention in that no appreciable interaction occurs between themicrowave generators 56 supplying the several waveguides, a conditionwhich is not present where conventional structure is employed.

While the invention has been herein described with reference to certainexemplary embodiments, it will be apparent that many variations andmodifications are possible within the scope of the invention and thus itis not intended to limit the invention except as defined in thefollowing claims.

What is claimed is:

1. Apparatus for treating products with microwave energy comprising, incombination, a long tunnel structure having conducting walls and forminga microwave chamber, means at each end of said chamber for suppressingthe emission of microwave energy therefrom, a conveyer extending throughsaid tunnel structure for carrying said :products therethrough, at leastone long waveguide extending along a substantial portion of the tunneland having a sidewall facing products carried on said conveyor, saidsidewall having open areas distributed along a substantial portion ofthe length thereof and constituting a non-resonant array for emittingmicrowave energy into said chamber, a microwave source coupled to saidwaveguide, and a plurality of spaced apart electrical- 1y conductivereflector elements transversely disposed in said tunnel between saidwaveguide and said conveyer.

2. In apparatus for treating products by microwave irradiation, thecombination comprising a housing having electrically conducting wallsand forming a microwave chamber, a conveyer extending through saidhousing for carrying said products therethrough, a waveguide extendingalong at least a portion of said chamber along the path of said conveyerand having an electrically conducting wall which is open to said chamberat least at spaced apart points along an extensive portion of the lengththereof, and a plurality of spaced apart electrically conducingreflector plates disposed in said chamber in proximity to said wall ofsaid waveguide and in substantially perpendicular relationship thereto,said plates being distributed along said path of said conveyer.

3. In apparatus for irradiating products with microwave energy, thecombination comprising a processing chamber formed of electricallyconducting material and having product input and output openings, meansfor conveying the products through said chamber along a path of travelfrom said input to said output openings, a mic-rowave guide extendingalong at least a portion of said chamber and having an electricallyconductive wall facing said path of travel and electrically open to saidchamber at each of a plurality of positions distributed along said pathof travel and spaced apart therealong by other than half the wavelengthin said guide to form a non-resonant array tending to radiate energyinto said chamber in inclined relation to said wall, a source ofmicrowave energy coupled to said guide, and reflector means fixed insaid chamber having electrically conductive reflector material disposedsubstantially transversely to said path of travel and in spaced relationto products carried along said path of travel, whereby precision tuningis rendered unnecessary because of said non-resonant array and wherebysaid reflector material acts to control the distribution of microwaveenergy radiated into said chamber by said nonresonant array.

4. In apparatus for irradiating products with microwave energy, thecombination comprising a microwave generator, a processing chamberformed of electrically conducting material and having product input andoutput openings, means for conveying the products through said chamberalong a path of travel from said input to said output opening, and anelongated microwave guide having one end thereof coupled to saidgenerator for excitation thereby, said guide extending along at least aportion of said chamber and having an electrically conductive wallfacing said path of travel and electrically opened to said chamber ateach of a plurality of apertures which are distributed along saidelongated guide and along said path of travel and which have sizes andspacings forming a non-resonant array, whereby the output of microwaveenergy from said generator is divided into a plurality of incrementswhich are injected into said chamber from successive ones of theapertures in said wall of said elongated guide as said output of energytravels along said guide from said one end thereof.

5. In apparatus for treating substances with microwaves, the combinationas set forth in claim 4 further including dielectric material physicallyscreening the interior of said guide from the interior of said chamberat the sites of said apertures while permitting injection of saidmicrowave energy into said chamber through said apertures and saidmaterial.

6. In apparatus for treating substances with microwaves, the combinationas set forth in claim 4 wherein the sizes and spacings of said aperturesat successive positions along said guide are of values which increasethe percentage of available microwave power injected into said chamberfrom said guide in direction along said guide away from said one endcoupled to said generator, said increase being by predetermined amountswhich divide the output of microwave energy from said generatorsubstantially evenly along a predetermined length of said elongatedprocessing chamber.

7. In apparatus for treating substances with microwaves, the combinationas set forth in claim 6 wherein said apertures include apertures ofdifie-rent sizes, said sizes becoming larger in said direction away fromsaid one end coupled to said generator.

8. In apparatus for treating substances with microwaves, the combinationas set forth in claim 6 wherein the spacings between said aperturesinclude different spacings, said spacings becoming smaller in saiddirection away from said one end coupled to said generator.

References Cited by the Examiner UNITED STATES PATENTS 2,389,606 4/1946Wang 219-1055 I 1 0 7 2,560,903 7/1951 Stiefel 219-1055 2,585,970 2/1952Shaw 219-1055 2,599,033 6/1952 Wild 219-1055 3,166,663 1/1965 Fritz219-1055 3,171,009 2/1965 Scheller et al. 219-1055 FOREIGN PATENTS652,223 11/1962 Canada. 664,730 6/ 1963 Canada. 979,577 4/1951 France. 0930,311 7/1963 Great Britain.

OTHER REFERENCES Fritz: German printed application No. 1,095,428 (KLRICHARD M. WOOD, Primary Examiner.

20 L. H. BENDER, Assistant Examiner.

4. IN APPARATUS FOR IRRADIATION PRODUCTS WITH MICROWAVE ENERGY, THECOMBINATION COMPRISING A MICROWAVE GENERATOR, A PROCESSING CHAMBERFORMED OF ELECTRICALLY CONDUCTING MATERIAL AND HAVING PRODUCT INPUT ANDOUTPUT OPENINGS, MEANS FOR CONVEYING THE PRODUCTS THROUGH SAID CHAMBERALONG A PATH OF TRAVEL FROM SAID INPUT TO SAID OUTPUT OPENING, AND ANELONGATED MICROWAVE GUIDE HAVING ONE END THEREOF COUPLED TO SAIDGENERATOR FOR EXCITATION THEREBY, SAID GUIDE EXTENDING ALONG AT LEAST APORTION OF SAID CHAMBER AND HAVING AN ELECTRICALLY CONDUCTIVE WALLFACING SAID PATH OF TRAVEL AND ELECTRICALLY OPENED TO SAID CHAMBER ATEACH OF A PLURALITY OF APERTURES WHICH ARE DISTRIBUTED ALONG SAIDELONGATED GUIDE AND ALONG SAID PATH OF TRAVEL AND WHICH HAVE SIZES ANDSPACINGS FORMING A NON-RESONANT ARRAY, WHEREBY THE OUTPUT OF MICROWAVEENERGY FROM SAID GENERATOR IS DIVIDED INTO A PLURALITY OF INCREMENTSWHICH ARE INJECTED INTO SAID CHAMBER FROM SUCCESSIVE ONES OF THEAPERTURES IN SAID WALL OF SAID ELONGATED GUIDE AS SAID OUTPUT OF ENERGYTRAVELS ALONG SAID GUIDE FROM SAID ONE END THEREOF.